public synchronized WhiteboardObject getWhiteBoardObjectListByRoomIdAndWhiteboard(Long room_id, Long whiteBoardId){
WhiteboardObjectList whiteboardObjectList = whiteBoardObjectList.get(room_id);
if (whiteboardObjectList == null) {
whiteboardObjectList = new WhiteboardObjectList();
}
WhiteboardObject whiteboardObjects = whiteboardObjectList.getWhiteboardObjects().get(whiteBoardId);
if (whiteboardObjects == null) {
whiteboardObjects = new WhiteboardObject();
}
return whiteboardObjects;
}